Abstract

Inner‐source pickup ions have been investigated by several workers who all assumed an initial velocity
distribution function which is dominated by high velocities in the solar wind
velocity frame. This non‐thermal velocity distribution is supposed to be due to the Lorentz force which acts on the freshly ionized particles. However, the location where inner‐source pickup ions are ionized lies close to the Sun (probably between 5 and
). The magnetic field and solar wind
velocity are near radial there and the Lorentz force acting on freshly created ions is small. Particles sputtered or ejected with small relative velocities (E<few eV) from interplanetary dust particles only experience a very small mirror force in the inner heliosphere which only succeeds to accelerate a very small fraction of them out of the solar vicinity after typically tens of hours to days. This would result in a higher charge state than observed for heavy ions and further aggravates the problem of the high abundance of inner‐source pickup ions.

Of course, the principal acceleration agent for inner‐source pickup ions has to be wave‐particle interactions in the inner heliosphere. As freshly created pickup ions encounter a wave, their pitch angle is scattered and they will, in most cases, experience a net gain in momentum which carries them outwards, out of the solar system. As we will show, inner‐source pickup ions are thus highly sensitive probes of the turbulent microstate of the inner heliosphere.